Location determination of wireless devices is typically employed for locating objects attached with these devices. Such objects may be people, specifically those who might need assistance, animals, pets, vehicles, mobile assets or other valuable items.
The present art provides powerful means for location determination of wireless devices. For example, a mobile (cellular) phone embedded with a GPS (Global Positioning System) receiver can be located practically worldwide. Such a device can be easily carried by a person and operate on a matchbox size battery for several days, before recharged.
However, some applications cannot bear the size or price or limited battery life of such a locatable wireless device. For example, it is not practical to attach a mobile phone to a dog or cat for locating so. Such a locatable device would be probably considered too large and too expensive and too often requiring battery recharge or replacement.
Some prior art inventions suggest a locatable device excluding a wide area transmitter, employing a positioning component such as GPS receiver, coupled with a short range transmitter which can access external devices to display or further communicate the location. Two such inventions are disclosed in the following U.S. patent applications.
U.S. patent application Ser. No. 20030132861 to Shieh discloses a GPS receiver with IR transmitter, adapted to transmit location signals to a nearby device.
U.S. patent application Ser. No. 20080001816 to Wang discloses a portable wireless earphone with a GPS and a Bluetooth wireless module.
Still, comprising a GPS receiver in a locatable device can be too expensive, power consuming, and bulky for some applications. Furthermore, a GPS receiver requires line of sight (LOS) with GPS satellites, thus it's not practical, for example, to place it in a rifle butt, or article in a store, or skier's gear to be tracked upon a snow avalanche.
Other prior art inventions suggest locatable devices excluding built in positioning components, avoiding related costs and power consumption and LOS restrictions. For example, “network based” location methods employed in cellular networks, where a mobile device transmission is detected by typically three base stations, and upon measuring the Time of Arrival (TOA) or Time Difference of Arrival (TDOA) or Angle of Arrival (AOA) of the same signal at these base stations, the mobile device location can be determined.
Still, the wide area transceiver comprised in such mobile devices might be considered too power consuming and too expensive for some applications, such as tracking pets or guns.
Other inventions suggest wirelessly locatable devices which avoid expensive and power consuming positioning components, and also do not use expensive and power consumption transmitters. Some present art technologies such as RFID (Radio Frequency Identification) enable detection and location determination of fingernail size devices that cost some cents, possibly operating many years on a small low cost battery and sometimes even with no battery at all. However, such devices can be read, i.e. located, only a few meters away from a compatible reader.
When an object is to be located in a local area, such as a building or a manufacturing plant or by a traffic toll checkpoint, short range devices might be well used, yet if an object is required to be located over a wide area, e.g. city or country, as in case of a lost dog or stolen car, short range devices are not suitable unless a dense network or readers/antennas/repeaters is deployed, which is often impractical and uneconomical.
Further art was suggested to locate low cost and low power wireless devices, over a wide area, by deploying discrete short range readers which can detect such devices in their vicinity, and report said presence to a remote control station.
U.S. Pat. No. 7,130,646 and U.S. patent application Ser. No. 20040162084 to Wang disclose a method of Positioning with wireless local area networks and WLAN-aided global positioning systems. When associated with a WLAN, a wireless device can quickly determine its relative and/or coordinate position based on information provided by an access point in the WLAN. The WLAN can periodically provide time, location, and decoded GPS data to the wireless device, significantly reducing the time to acquire the necessary GPS satellite data to determine its coordinate position.
Still, Wang's invention employs substantially complex wireless devices, a terrestrial infrastructure, and is actually oriented to assist self location determination at a wireless device rather than determine a wireless device's location at a remote station.
U.S. Pat. No. 6,246,882 to Lachance discloses a system and method for wide area item tracking, attaching an RFID to each item to be tracked. The wide area of the system includes a plurality of handling zones, such as a truck or a manufacturing plant, where items are manipulated or transported during the delivery or shipping process. When the item is moved past a handling zone interrogator into a new handling zone, an RFID reader detects the item ID. A mobile station connected to the RFID reader transmits a signal containing the item ID and an identification of the handling zone over a cellular network, to a remote database.
Lachance's invention enables tracking of low power devices, yet limited to a cellular network cell resolution, and on sporadic regions (warehouse, manufacturing plant, etc') only.
Further inventions suggest adding more accurate positioning facilities to short range readers, so location determination of nearby wireless devices detected by those readers would be refined.
U.S. patent application Ser. No. 20030001775 and U.S. Pat. No. 6,657,586 to Turner disclose a system and method for locating an object, comprised of a plurality of tag readers that receive wireless tag signals from a tag transmitter coupled with an object to be located. Tag signals include ID data, each tag signal reader includes a GPS receiver and a wireless transmitter to transmit tag ID and location of tag reader, to a remote processor, which determines which tag signals are first-to-arrive signals and conducts differentiation of the first-to-arrive signals to locate a tag transmitter and object coupled therewith.
Still, Turner's methods require substantial terrestrial infrastructure, which normally limit the operating area coverage, and generate considerable interrogation transmissions.
Then, in order to cover a wide area for locating low cost and low power wireless devices, without deploying further dense terrestrial infrastructure, mobile access points were been suggested. Such mobile access points could detect short range transmissions from nearby low power wireless devices, and communicate these signals to a remote control station, over a wide area network.
U.S. Pat. No. 7,155,238 to Katz discloses a system and method for location determination of wireless devices based on two layers of communication infrastructure: a fixed network and a mobile network. This invention teaches how a multitude of mobile devices, such as Bluetooth enabled cellular phones, can serve as access points for short range wireless devices, Bluetooth compatible in this example, and communicate their presence to a remote destination. Further, the location of such a short range wireless device can be determined by determining the location of the mobile device which served as its access point, and since this can be well done by present art methods (e.g. mobile device embedded with GPS receiver), the wireless device does not have to obtain built in location determination circuitry and can be substantially small, low cost and low power.
Nevertheless, due to the short range nature of low power wireless devices, and since wireless and mobile devices (including mobile access points) might move dynamically (carried by people, animals vehicles, etc'), it is crucial to establish a swift ad-hoc connection between such devices in order to enable location determination of a wireless device. For example, a mobile device installed in a driving car and a wireless device embedded in a dog's collar, might have a chance to establish a wireless connection for only less than a second, while momentarily staying in communications range, e.g. up to fifty meters apart. In order not to miss this chance, it would be desirable if one of these devices often transmits a searching signal while the other is trying to receive such. However, such as strategy might significantly reduce battery life and cause much noise and interference. On the other hand, putting receivers and transmitters often to sleep as often done for saving battery power, significantly reduces the chance to establish a rapid ad-hoc connection.
In this context, U.S. Pat. No. 7,155,238 does not teach how can an ad-hoc short range connection between a wireless device and a mobile device be rapidly established, while achieving substantial battery life at a wireless device, for example several years of operation on a small low cost battery. This is neither taught by other patents mentioned above.
If a wireless device is required to operate on a small battery for several years, as would be the case with a locatable device attached to a dog or a cat or a gun, then power consumption should be carefully considered, normally causing the device to stay most to the time asleep, i.e. in deep power save mode. For example, a typical lithium battery of size ½ AA (cylinder shape, about 14 mm base diameter and 25 mm height) and nominal voltage of 3.6 V, obtains a capacity of about 1 Ah, thus enables 5 years of operation at an average current consumption of about 23 micro amperes (0.023 milliamps). But even a low power receiver such as Bluetooth (reference—www.csr.com) consumes at least several milliamps when active, and more than 0.5 milliamps in inquiry/inquiry scan modes, searching for ad-hoc connections (further information on Bluetooth can be found at www.bluetooth.com and http://en.wikipedia.org/wiki/Bluetooth). Even “conditional scan” mode, searching for RF activity on Bluetooth bands, requires much more power from the scanning device and obviously additional power is consumed and dissipated by the inquiring transmitter until an ad-hoc connection is accomplished. Furthermore, inquiry and inquiry scan operations might last a long time until succeed, due to uncertainties in space (out of range) and time (unsynchronized clocks) and frequencies (different hopping patterns) and mode (which device inquires and which one is scanning for inquiry), between two unconnected Bluetooth devices. During these long periods, batteries are wasted and interfering signals are generated, undesirably.
Specifically, the process of establishing a wireless connection between unsynchronized frequency hopping devices is not straight forward. The following paper, for example, studies ad hoc networking with Bluetooth, to find an efficient way of discovering neighbor devices. Based on real-world measurements and simulations, the researches derive optimal parameters for symmetric ad hoc neighbor discovery, using standard Bluetooth procedures (inquiry and inquiry scan). The results show a mean neighbor discovery delay of about 8 seconds. Clearly, such a long discovery time is undesirable for devices installed in driving cars or so, and as indicated before, this period of time can become even longer when such devices move away and often go to sleep in order to save battery power.    Paper: Performance of Symmetric Neighbor Discovery in Bluetooth Ad Hoc Networks    Diego Bohman, Matthias Frank, Peter Martini, Christoph Scholz    Institute of Computer Science IV, University of Bonn, R{umlaut over ( )}omerstraβe 164, D-53117 Bonn    http://web.informatik.uni-bonn.de/IV/Mitarbeiter/scholz/10 Bohman.pdf
The following invention suggests a location method with fast detection of moving wireless devices, enabling significant power consumption saving.
U.S. Pat. No. 4,649,385 to Aires et al. discloses a method for determining the location of a transceiver unit throughout a defined facility. A central station establishes communications with one or more relay stations, searching for a particular unit over that area, the relay stations respond by sending out wake-up signals and radiant energy inquiry signals. The individual unit identified in the inquiry signal responds with a radiant energy acknowledgement signal. Embodiments of the invention disclose the use of infrared energy or ultrasonic energy for the radiant energy. The relay stations report to the central station whether the individual unit acknowledged the searching signal.
Aires' method enables location determination of low power devices, yet it requires a significant terrestrial infrastructure and would be typically restricted to local areas such as a hospital, an airport, a department store, a large legal office, a manufacturing complex, etc', but is not practical for wide area (e.g. city, country) location determination. In addition, similarly to RFID methods, detection range is quite limited due to the nature of wireless communications employed. Furthermore, much inefficient radiation is emitted by the relay station/interrogator/reader, since it has no prior knowledge indicating a potential presence of a nearby wireless device, therefore constantly transmitting interrogation signals.
The present are methods described above have not yet provided satisfactory solutions to the problem of location determination of low power wireless devices over a wide area.
It is an object of the present invention to provide a system and method for location determination of wireless devices over a wide area.
It is another object of the present invention to provide a system and method for location determination of wireless devices over a wide area, enabling low power consumption devices.
It is also an object of the present invention to provide a system and method for location determination of wireless devices over a wide area, enabling low cost devices.
It is yet another object of the present invention to provide a system and method for location determination of wireless devices over a wide area, enabling small and lightweight devices.
It is also an object of the present invention to provide a system and a method for location determination of wireless devices over a wide area, by leveraging present accurate location determination systems such as GPS and cellular network based methods.
It is still another object of the present invention to provide a system and method for location determination of wireless devices over a wide area, minimizing deployment of further communications networking infrastructure.
It is yet another object of the present invention to provide a system and method for location determination of wireless devices over a wide area, avoiding as much as possible inefficient transmissions which cause interference and jamming and noise.
Other objects and advantages of the invention will become apparent as the description proceeds.